1. Introduction
This invention relates to coated fabrics used in the reinforcement of resin-bonded abrasive wheels.
2. Description of the Prior Art
Resin-bonded abrasive wheels are well-known in the art and described in numerous publications. They are used for a variety of purposes such as the cutting of various materials including metals and concrete, for grinding, sanding, buffing and other procedures known to the art. Typically, resin-bonded abrasive wheels may be reinforced with various materials such as random fibers and variously shaped woven and non-woven fabrics. Exemplary fabric materials comprise cotton, nylon, glass, rayon and aramid such as that marketed under the trade name Kelvar. These reinforcements provide a margin of safety in the event that the abrasive wheel cracks or breaks during use and thereby increase the safe operating speed and efficiency of the wheel.
It is known in the art that when woven fabric is used as a reinforcing material for an abrasive wheel, the fabric is coated with a resin to protect the fibers from degradative abrasive attack by the abrasive particles during molding, to allow proper bonding between the resin in the wheel and the fabric reinforcement and to prevent the fabric from distorting. The resins most frequently used for such purposes are the phenolic resins, most often the phenol formaldehyde resins. The protection of fabric, particularly glass fabric, with thermosetting phenolformaldehyde resins prior to preparation of an abrasive wheel is illustrated in U.S. Pat. Nos. 2,745,224; 2,808,688; and U.S. Pat. No. Re 25,303, each of which is incorporated herein by reference.
For preparing coated fabrics for the reinforcement of abrasive wheels, it is believed that only thermosetting resins are used. The most commonly used resins are the resole phenolics which will cure to form an infusible three-dimensional matrix upon heating. The resole resins are known by such names as single-stage, one-step and reactive resins. Less frequently, novolak type phenolic resins have been used for coating fabrics in the preparation of reinforcing discs, but always in combination with a crosslinking agent such as hexamethylenetetramine so that upon heating, the resin will cure and form a three-dimensional crosslinked matrix. In such case, the novolak is a thermosetting material. Typically, from 5 to 15% by weight hexamethylenetetramine is added to the novolak resin. The combination of the novolak resin and the crosslinking agent is typically identified as a two-step or two-stage resin.
A problem encountered with known resin-coated or impregnated fabric reinforcements is that with extended storage before use, the fabrics stiffen and lose their desirable flow characteristics. This results in poorer performance possibly as a consequence of a decrease or loss of chemical bond between the resin matrix for the abrasive particles and the resin coating over the reinforcing fabric. As a consequence, the useful life of the reinforcement is limited significantly, and wheels made with aged reinforcements of this type may not be satisfactory in performance or safety, in the case of wheels made by the "cold press" method.